Light guide panel, surface light source apparatus including light guide panel, and flat panel display including surface light source apparatus

ABSTRACT

A light guide panel includes: a light guide layer having a light incident surface; a polarization separation layer configured to select a desired polarization among light emitted from the light guide layer and to emit light having the polarization; and a light homogenization layer including a plurality of fibers and a supporting medium of the fibers, the light homogenization layer configured to diffuse and scatter light incident on the light guide layer into the light guide layer. The polarization separation layer includes: a plurality of first fibers having birefringence; and a first supporting medium that is isotropic and configured to support the first fibers. The refractive index of the first supporting medium corresponds to at least one of two different refractive indices of the first fibers. The light homogenization layer includes: a plurality of second fibers having birefringence; and a second supporting medium that is isotropic and configured to support the second fibers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No.2011-0140649, filed on Jun. 24, 2011, and Korean Patent Application No.10-2012-0005277, filed Jan. 17, 2012, the disclosure of each of which isincorporated herein in its entirety by reference.

BACKGROUND

1. Field

The present disclosure relates to display apparatuses and moreparticularly, to light guide panels, surface light source apparatusesincluding the light guide panels, and/or flat panel displays includingthe surface light source apparatuses.

2. Description of the Related Art

Liquid crystal displays used in personal computers (PCs), computermonitors, liquid crystal display (LCD) TVs, mobile communicationterminals, or the like are light-receiving displays that do not emitlight by themselves but display images by selectively transmitting lightirradiated from the outside. Thus, a backlight is included on a rearsurface of the liquid crystal displays as a surface light sourceapparatus.

In the liquid crystal displays, light emitted from the surface lightsource apparatus transmits through a liquid crystal layer arrangedbetween a pair of polarization plates that have transmission axes atright angles to each other. An image is displayed as the light thattransmits through the liquid crystal layer is electrically turned on oroff.

An absorption-type polarization plate is used as the polarizationplates. In the absorption-type polarization plate, an iodine-coloreduniaxially oriented polyvinyl alcohol film is used as a polarizer. Aprotection film such as triacetyl cellulose film or the like, and acoating layer formed of an acrylic resin, or a phase difference filmsuch as norbornene or polycarbonate is formed on one or both sides ofthe polarizer.

The absorption-type polarization plate transmits only light in adirection of a transmission axis of the polarization plate and absorbsthe other components of light. Thus, in principle, light usageefficiency thereof (light transmittance) does not exceed 50%. Moreover,considering that reflectivity of an inner surface of the absorption-typepolarization plate is 4%, the light usage efficiency of theabsorption-type polarization plate is 46% at the greatest. Thus, toachieve low power consumption by liquid crystal displays, an efficientuse of the backlight and an improvement in luminance are desirable.

As one of the methods for solving the above-described problem, areflective polarization plate that uses optical reflection andinterference is known. The reflective polarization plate reflects adesired polarization component light and transmits polarization of theopposite property to the desired polarization component light.

An axis of the reflective polarization plate is adjusted such that onlypolarization in a transmission axis direction is transmitted so that thelight transmitted through the reflective polarization plate remains thesame as linear polarization, and at the same time, the absorbedpolarization is reflected for reuse in the absorption-type polarizationplate. Thus, light usage efficiency of light emitted from the backlightmay be improved.

An example of the reflective polarization plate is a dual brightnessenhancement film (DBEF) including refractive index isotropic layers andrefractive index anisotropic layers that are alternately stacked.However, a DBEF requires polymer films of several hundreds of stackedlayers in total in order to provide polarization over a visible region.Thus, precise control is needed and this increases manufacturing costs.

To improve light usage efficiency and polarization separation power morecost-effectively, a technique of using a polarization sensitivescattering element (PSSE) is being researched. For example, Prior Art 1(Japanese Patent Publication No. Hei 11-502036) discloses a method inwhich a polarization component in a direction perpendicular to atransmission axis is scattered to the backside by using a PSSE, and apolarization state of a corresponding backside scattering component isconverted by using a ing s of stacked lay

In addition, Prior Art 2 (Japanese Patent Publication No. 2009-047802)discloses a reflective polarization plate in which a birefringent bodyformed of fibers having birefringence is used as a PSSE. In thereflective polarization plate, a layer in which a refractive index in across-sectional direction of the birefringent body (ordinary rayrefractive index) corresponds to a refractive index of a supportingmedium (polarization layer A) and a layer (polarization layer B) inwhich a refractive index in a length direction of the birefringent body(ordinary ray refractive index) corresponds to a refractive index of asupporting medium are alternately stacked such that arrangementdirections of the birefringent bodies cross each other. Accordingly,polarization separation with respect to light that is obliquely incidentor diffused light is improved.

In addition, Prior Art 3 (Japanese Patent Publication No. 2006-517720)discloses a method of improving polarization separation efficiency byscattering only one component of polarization and emitting the same tothe outside by integrating an isotropic resin layer, in whichbirefringence fibers are buried as a PSSE, into a light guide panel.

To reduce power consumption of the surface light source apparatuses,LEDs having a long life span and power consumption reduction effect arefrequently used as a backlight.

SUMMARY

At least one example embodiment including light guide panels forimproving polarization separation efficiency and preventing luminancespots even when a discontinuous light source is disposed on across-section of the light guide panels is provided.

At least one example embodiment including surface light sourceapparatuses including the light guide panels is provided.

At least one example embodiment including flat panel displays includingthe surface light source apparatuses as a light source apparatus isprovided.

Additional example embodiments will be set forth in part in thedescription that follows and, in part, will be apparent from thedescription, or may be learned by practice of the presented exampleembodiments.

According to an example embodiment, a light guide panel includes: alight guide layer including a light incident surface; a polarizationseparation layer configured to select a desired polarization among lightemitted from the light guide layer and to emit light having thepolarization; and a light homogenization layer including a plurality offirst fibers and a first supporting medium of the first fibers, thelight homogenization layer configured to diffuse and scatter lightincident on the light guide layer into the light guide layer.

The polarization separation layer may include: a plurality of secondfibers having birefringence; and a second supporting medium that isisotropic and configured to support the second fibers.

A refractive index of the second supporting medium may correspond to atleast one of two different refractive indices of the second fibers.

The plurality of first fibers have birefringence and the firstsupporting medium is isotropic and configured to support the firstfibers.

A refractive index of the first supporting medium may be different fromat least one of the two different refractive indices of the firstfibers.

A surface roughness Rz of an outer circumferential surface of the secondfibers may be from about 0.1 μm to about 10 μm.

The second fibers may have a polygonal cross-section in a radiusdirection.

One of the light guide layer, the polarization separation layer, and thelight homogenization layer may be between the remaining two layers.

The light guide panel may further include: a phase difference plateconfigured to convert a polarization direction of light in the lightguide layer; and a reflection plate on a surface except the lightincident surface and a light emitting surface of the light guide layer,the reflection plate configured to reflect light emitted from the lightguide layer back into the light guide layer.

The polarization separation layer and the light homogenization layer maybe stacked on the light emitting surface of the light guide layer. Thepolarization separation layer and the light homogenization layer may beintegrated into a single layer. In the single layer, the first fibersand the second fibers may alternate, and a third supporting medium mayinclude the first and second supporting media that supports the firstand second fibers.

The first fibers and the second fibers may be different materials.

The light guide layer may be a same material as at least one of thefirst and second supporting media.

A density of the second fibers may be higher away from the lightincident surface.

A density of the first fibers may vary according to arrangementpositions.

Some of the plurality of first and second fibers may includediscontinuous portions.

Portions of the plurality of first and second fibers may be overlapped.

According to another example embodiment, a surface light sourceapparatus including: a light source unit including a plurality of lightsources spaced apart from one another; and a light guide panelconfigured to emit light having a polarization component of lightincident from the light source unit, wherein the light guide panel isone described above.

A density of the first fibers may be higher between the plurality oflight sources.

The plurality of light sources may be on two opposite sides of the lightguide panel.

According to another example embodiment, a flat panel display includes:a light source apparatus; and a liquid crystal panel configured todisplay an image by using light supplied from the light sourceapparatus, wherein the light source apparatus is the surface lightsource apparatus described above.

According to some example embodiments, light is scattered and diffusedat various angles in an in-plane direction via a light homogenizationlayer in which first fibers extended vertically to an incident surfaceare arranged. Thus, even when a discontinuous light source is used,uniform luminance may be obtained.

By using a polarization separation layer in which second fibers extendedparallel to an incident surface are arranged, only desired polarizationcomponents may be selectively emitted with a high polarizationseparation efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the example embodiments,taken in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of a surface light source apparatusaccording to an example embodiment;

FIGS. 2A and 2B are schematic views illustrating an example of arelationship between a fiber and a refractive index;

FIG. 3 is a cross-sectional view illustrating a modified example of across-section of the fiber shown in FIG. 2A;

FIG. 4A is a right-side cross-sectional view illustrating the surfacelight source apparatus of FIG. 1;

FIG. 4B is an expanded view of FIG. 4A illustrating propagation of anS-polarization component incident to a polarization separation layer;

FIG. 4C is an expanded view of FIG. 4A illustrating propagation of aP-polarization component incident to the polarization separation layer;

FIG. 5 is a bottom view of the surface light source apparatus of FIG. 1;

FIG. 6 is a side view of a surface light source apparatus according toanother example embodiment;

FIG. 7 is a side view of a surface light source apparatus according toanother example embodiment;

FIG. 8 is a side view of a surface light source apparatus according toanother example embodiment;

FIG. 9 is a side view of a surface light source apparatus according toanother example embodiment;

FIG. 10 is a side view of a surface light source apparatus according toanother example embodiment;

FIG. 11 is a side view of a surface light source apparatus according toanother example embodiment;

FIG. 12 is an image of a cross-section of a polarization separationlayer formed in a surface light source apparatus according to anotherexample embodiment;

FIG. 13 an image illustrating two-dimensional luminance distribution oflight emitted through an image plane of a light guide panel(light-emitting surface) of a surface light source apparatus accordingto another example embodiment; and

FIG. 14 an image illustrating two-dimensional luminance distribution oflight emitted through an image plane of a light guide panel(light-emitting surface) of a surface light source apparatus accordingto a comparative example.

DETAILED DESCRIPTION

Reference will now be made in detail to example embodiments, examples ofwhich are illustrated in the accompanying drawings, wherein likereference numerals refer to like elements throughout. In thisspecification, thicknesses of layers or regions illustrated in thedrawings are exaggerated for clarity of description. In addition,measurement ratios in the drawings are exaggerated for convenience ofdescription and may vary from actual ratios. In this regard, the exampleembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theexample embodiments are merely described below, by referring to thefigures, to explain aspects of the present description. As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items. Expressions such as “at least one of,” whenpreceding a list of elements, modify the entire list of elements and donot modify the individual elements of the list.

When a (e.g., layer, region, or plate) is referred to as being herein“on,” “connected to,” or “coupled to” another member, the member may bedirectly on, or connected or coupled to the another member orintervening member(s) between the member and the another member may bepresent.

A surface light source apparatus according to some example embodimentswill be described.

FIG. 1 is a perspective view of a surface light source apparatus 1according to an example embodiment.

FIGS. 2A and 2B are schematic views illustrating an example of arelationship between a fiber and a refractive index, and FIG. 3 is across-sectional view illustrating a modified example of a cross-sectionof the fiber.

As illustrated in FIG. 1, the surface light source apparatus 1 is anedge light type surface light source apparatus. The surface light sourceapparatus 1 includes a light source unit 10 and a light guide panel 20transmitting a desired polarization component among the light emittedfrom a plurality of light sources 11 of the light source unit 10. In anexample embodiment, light is emitted as surface emission from thesurface light source apparatus 1 in an upward direction of FIG. 1.Although not shown in FIG. 1, when the surface light source apparatus 1is applied to a liquid crystal display, a liquid crystal unit may bearranged on a surface of the surface light source apparatus 1 from whichlight is emitted.

The light source unit 10 emits light to be supplied in the surface lightsource apparatus 1 and the light source unit 10 is on a side of thelight guide panel 20. The light source unit 10 includes a plurality oflight sources 11 arranged at intervals. The intervals between theplurality of light sources 10 may be regular or irregular.

While the plurality of light sources 11 are arranged one-dimensionallyin FIG. 1, they may also be arranged two-dimensionally. For example, theplurality of light sources 11 may be point light-emitting diodes (LEDs).

The light guide panel 20 may include a rectangular parallelepiped plate.The light guide panel 20 includes a light guide layer 30, a polarizationseparation layer 40 stacked on the light guide layer 30, a lighthomogenization layer 50 stacked on the light guide layer 30, and a phasedifference plate 60 and a reflection plate 70 on the light guide layer30. The polarization separation layer 40 and the light homogenizationlayer 50 face each other with the light guide layer 30 interposedtherebetween. The light guide layer 30 allows light emitted from thelight source 11 to be incident to an incident surface 30 a, which is aside surface thereof, and enter the light guide panel 20. The enteredlight is propagated in the light guide layer 30 and only a desiredpolarization component is selectively emitted from the polarizationseparation layer 40. The light guide layer 30 may be formed of atransparent material capable of transmitting incident light. Thetransparent material may be, for example, an optical isotropic materialsuch as polymethyl methacrylate (PMMA) or polycarbonate (PC). Thepolarization separation layer 40 is stacked on the light guide layer 30.The polarization separation layer 40 derives desired polarization amongthe light in the light guide layer 30 from a light emitting surface 30 bof the light guide layer 30, which is a principal surface of the lightguide layer 30 on a side. The polarization separation layer 40 reflectspolarization light that is perpendicular to this derived polarization.The polarization separation layer 40 may be on an outer surface of thelight guide layer 30 but is not limited thereto.

The polarization separation layer 40 may include a first fiber 41 and afirst supporting medium 42 that supports the first fiber 41. Forexample, the first fiber 41 may extend parallel to the incident surface30 a of the light guide layer 30, or may extend in a direction which isinclined by about ±45° with respect to the direction parallel to theincident surface 30 a. The first fiber 41 may be provided in plural.That is, the polarization separation layer 40 may include a plurality offirst fibers 41. The light homogenization layer 50 is stacked on thelight guide layer 30. The light homogenization layer 50 homogenizes alight direction by diffusing light in the light guide layer 30 in anin-plane direction, for example, in a direction perpendicular to a lightpropagation direction. The light homogenization layer 50 includes asecond fiber 51 and a second supporting medium 52 that supports thesecond fiber 51. For example, the second fiber 51 may extend in adirection perpendicular to the incident surface 30 a of the light guidelayer 30, or may extend in a direction which is inclined by about ±45°with respect to the direction perpendicular to the incident surface 30a.

The light homogenization layer 50 includes a plurality of second fibers51. The plurality of second fibers 51 are parallel to the incidentsurface 30 a of the light guide layer 30. For example, the second fibers51 are arranged in a direction perpendicular to the arrangementdirection of the first fibers 41 of the polarization separation layer40. The first and second fibers 41 and 51 of the polarization separationlayer 40 and the light homogenization layer 50 have birefringence. Thefirst and second fibers 41 and 51 have an extraordinary ray refractiveindex ne and an ordinary ray refractive index no. The refractive indexne is greater than the refractive index no.

The relationship between refractive indices of the first and secondfibers 41 and 51 will be described below with reference to FIGS. 2A and2B.

As illustrated in FIGS. 2A and 2B, the first and second fibers 41 and 51have the ordinary ray refractive index no in a cross-sectional directionthat is smaller than the extraordinary ray refractive index ne in alength direction. The first and second fibers 41 and 51 may be formed ofvarious materials having birefringence. For example, a polymer fiberthat is prepared by extending a polymer may be used for a stablecross-section, excellent durability, and easy orientationcharacteristics.

Examples of the polymer fiber may include polyolefin fibers such aspolyethylene (PE), polytetrafluoroethylene (PTFE), polypropylene (PP);polyvinyl fibers such as polyfluorinated vinylidene (PVdF),polyfluorinated vinyl (PVF), polyvinyl chloride (PVC), or polyvinylalcohol; and acrylic fibers such as polyacrylonitrile (PAN).

The polymer fiber may be aliphatic polyamide fiber such as Nylon 6 (N6),Nylon 6,6 (N66), Nylon 4,6 (N46), or Nylon 6,10 (N610); aromaticpolyamide fibers (aramid fiber) such as poly(m-phenyleneisophthalamide)(PMPIA) or poly(p-phenylene terephthalamide) (PMPTA); or polyesterfibers such as polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), or poly-),caprolactone.

The polymer fiber may be animal fibers such as silk, wool, or cobweb, orcellulose vegetable fiber such as cupra, rayon fibers, etc. The types ofthe first fiber 41 and the second fiber 51 may be selected to satisfythe relationship between refractive indices that will be describedbelow, or the same or different types may be used. Various types offibers may be used in the polarization separation layer 40 or the lighthomogenization layer 50.

The first and second fibers 41 and 51 may be formed of a polymer fiber.This polymer has a great refractive index difference An between anextraordinary ray refractive index ne and an ordinary ray refractiveindex no. The larger the refractive index difference Δn is, the moreimproved polarization separation efficiency of the polarizationseparation layer 40 or light diffusion efficiency of the lighthomogenization layer 50 may be. The difference An in the refractiveindices may be 0.03 or greater, and for example, 0.05 or greater or 0.1or greater.

The extraordinary ray refractive index ne and the ordinary rayrefractive index no of the polymer fiber may be controlled by adjustinga tensioning speed of a polymer, or a tensioning rate thereof, amaterial of the polymer, a thickness (diameter) or density of a fiber.

Table 1 below shows an extraordinary ray refractive index ne and anordinary ray refractive index no of representative draft polymer fibers.The refractive indices of Table 1 are calculated by dipping a fiber inliquids of various refractive indices, adjusting a liquid that isinvisible as fiber lines are assimilated with the liquid by using apolarization microscope, and measuring the refractive index of theadjusted liquid using Atagosa Digital Abbe Refraction System DRA1(wavelength: 589 nm). The refractive index of the adjusted liquid may bemeasured with respect to each of transmission axes of polarization tomeasure no and ne.

TABLE 1 Ordinary ray refractive index no and extraordinary rayrefractive index ne of representative polymer fibers Thickness MaterialAbbreviation (μm) no ne Δn Nylon 6 N6 75 1.5182 1.6228 0.1046 Nylon 6 N690 1.5182 1.6104 0.0922 Nylon 6,10 N610 50 1.5217 1.5711 0.0494 Nylon6,10 N610 100 1.5217 1.5711 0.0494 Nylon 6,6 N66 100 1.5182 1.59710.0789 Polyfluorinated PVdF 70 1.4193 1.4501 0.0308 vinylidenePolyethylene PET 16 1.5449 1.7200 0.1751 terephthalate

Thicknesses of the first and second fibers 41 and 51 may vary. Thethicknesses of the first and second fibers 41 and 51 may be controlledaccording to a size of a display to which they are applied. Thethicknesses of the first and second fibers 41 and 51 may be controlledto have desired refractive indices. For example, the thicknesses of thefirst and second fibers 41 and 51 may be from about 1 μm to about 200μm.

The intervals between the first and second fibers 41 and 51 may vary.The intervals between the first and second fibers 41 and 51 may beselected according to a size of a display and to be smaller than a pixelpitch of a liquid crystal display to which the first and second fibers41 and 51 are applied. The intervals between the first and second fibers41 and 51 may be regular or irregular. The first and second fibers 41and 51 may have a single-layer structure or a multi-layer structure.

The first fibers 41 may be arranged with uniform or non-uniform density.For example, the first fibers 41 may be arranged with a density thatincreases away from the light sources 11. For example, a density of thefirst fibers 41 in the polarization separation layer 40 may increasecontinuously or stepwise away from the light sources 11. A light amountis reduced away from the light sources 11. Accordingly, in an area witha small light amount and away from the light sources 11, the firstfibers 41 may be densely arranged. In an area with a large light amountnear the light sources 11, the first fibers 41 may be coarsely arranged.Accordingly, a uniform light may be emitted over the entire image plane(light-emitting surface) of the light guide panel 20.

Lengths of the first and second fibers 41 and 51 may be determinedaccording to a size of the polarization separation layer 40 or a size ofthe light homogenization layer 50 in which the first and second fibers41 and 51 are arranged. The lengths of the first and second fibers 41and 51 are not limited to being continuous in a longitudinal directionof the polarization separation layer 40 or the light homogenizationlayer 50. For example, some portions of the first and second fibers 41and 51 may be removed and discontinuous portions may be present. Some ofthe first and second fibers 41 and 51 may be overlapped. The first andsecond fibers 41 and 51 may have a circular cross-section as illustratedin FIG. 1 but are not limited thereto, and may have a differentcross-section. For example, as illustrated in FIG. 3, the first andsecond fibers 41 and 51 may have a regular or irregular polygonalcross-section such as a triangular, rectangular, or hexagonalcross-section, or a cross-section formed by combining a curved line anda straight line. “Polygonal cross-section” includes not only figuresrespective sides of which formed by straight lines, but also figuresrespective sides of which are formed by curved lines. For example,polygonal cross-sections of the first and second fibers 41 and 51 mayhave some curved lines on each side or on each vertex, and thesecross-sections are also included in the above-described “polygonalcross-section.”

As will be described below, in the polarization separation layer 40,only a desired polarization component of light is selectively scatteredby the first fibers 41, and emitted from the light emitting surface 30b. The light is likely to scatter in a light guide direction, and thus,the amount of scattered light in a direction perpendicular to a lightproceeding direction is reduced.

When a surface light source apparatus including a light guide panelaccording to an example embodiment is used as a backlight of a liquidcrystal display, and if the first fibers 41 have a polygonalcross-section, various scattering angles are formed, and thus scatteringof light may increase in a direction perpendicular to the light guidedirection. As a result, light with a more uniform angle distribution maybe obtained.

Forms of external circumferential surfaces of the first and secondfibers 41 and 51 may vary. Surface roughness Rz of an outercircumferential surface of the first fibers 41 may be from about 0.1 μmto about 10 μm. Various light scattering angles are formed by the firstfibers 41, and thus, light with a more uniform angle distribution may beobtained. The e, tlight scattering angles are formed by the first fibers41, and thus, lined based on JIS B 0601-2001.

The first and second supporting media 42 and 52 support the first andsecond fibers 41 and 51, respectively, and may be formed of an opticallyisotropic material. Accordingly, the first and second supporting media42 and 52 may be formed of any material that has excellent adhesivenesswith respect to the first and second fibers 41 and 51 and opticaltransparency. For example, the first and second supporting media 42 and52 may be formed of a curable resin that is polymerable/linkable by heator radiation.

The curable resin may be, for example, a UV-curing resin formed of acompound including, for example, an acryloyl group, a methacryloylgroup, a vinyl group, an aryl group, a styryl group, a thiol group, anepoxy group, a vinyl ether group, or an oxetanyl group.

The curable resin may be a thermosetting resin formed of silicon resin,aryl ester, acrylic resin, epoxy resin, polyimide, or urethane resin.

The curable resin may be a compound of the UV-curing resin and thethermosetting resin.

The first and second supporting media 42 and 52 may be formed of anacrylic resin such as PMMA; a polyolefin resin such as PE, PP, orcycloolefin polymer (COP); a polyester resin such as PET; a polyethersuch as polyphenylene oxide (PPO); a vinyl resin such as polyvinylalcohol; polystyrene, PC, polyurethane, polyamide, polyimide, or epoxyresin; a copolymer including at least two types of monomers formingthese materials; or a blend of these polymers.

By mixing a plurality of resins, refractive indices (nm) of the firstand second supporting media 42 and 52 may be controlled as desired.

The polarization separation layer 40 may be formed such that arefractive index nm1 of the first supporting medium 42 matches anordinary ray refractive index no1 or an extraordinary ray refractiveindex ne1 of the first fiber 41.

An example embodiment in which the refractive index nm1 of the firstsupporting medium 42 and the ordinary ray refractive index no1 of thefirst fiber 41 match each other will be described.

In this specification, “the refractive indexes nA and nB match eachother” means that the refractive indexes nA and nB match each other witha precision to the second decimal point or greater, and this may alsoindicate that the refractive indexes nA and nB match each other with aprecision to the third decimal point or greater.

The light homogenization layer 50 may be formed such that a refractiveindex nm2 of the second supporting medium 52 is different from at leastone of an ordinary ray refractive index no2 and an extraordinary rayrefractive index ne2 of the second fiber 51.

An example embodiment in which the refractive index nm2 of the secondsupporting medium 52 is different from both the ordinary ray refractiveindex no2 and the extraordinary ray refractive index ne2 of the secondfiber 51 will be described.

A phase difference plate 60 is opposite to the incident surface 30 a ofthe light guide layer 30, and converts a polarization direction of lightpropagating in the light guide layer 30. The phase difference plate 60may be, for example, a λ/4 plate that shifts a phase by λ/4. The phasedifference plate 60 may be included selectively. Thus, the phasedifference plate 60 may also be omitted.

The reflection plate 70 prevents light in the light guide layer 30 fromleaking to other portions except through the light emitting surface 30b. To this end, the reflection plate 70 is stacked on a side except theincident surface 30 a of the light guide layer 30 or on a principalsurface of the light guide layer 30 that is opposite to the lightemitting surface 30 b. The reflection plate 70 is stacked on the phasedifference plate 60 or the light homogenization layer 50. Although notshown in the drawings, the reflection plate 70 may also be formed on twosurfaces besides the incident surface 30 a of the light guide layer 30and the opposite surface to the incident surface 30 a. Also, althoughnot shown in the drawings, the reflection plate 70 may be disposedbetween the plurality of light sources 11 or on or under the lightsources 11.

The principle of surface emission of light from a light source in thesurface light source apparatus 1 will be described.

FIG. 4A is a right-side cross-sectional view illustrating the surfacelight source apparatus 1 of FIG. 1. FIG. 4B is an expanded view of FIG.4A illustrating an example of propagation of an S-polarization componentincident to the polarization separation layer 40. FIG. 4C is an expandedview of FIG. 4A illustrating an example of propagation of aP-polarization component incident to the polarization separation layer40.

As illustrated in FIG. 4A, light is incident from the light source 11 onthe incident surface 30 a of the light guide layer 30. The incidentlight propagates through the light guide layer 30 by repetitive internalreflection on interfaces between the polarization separation layer 40,the light homogenization layer 50, and the phase difference plate 60 asdenoted by a chain line or a long-and-short broken line. Light isreflected by the reflection plate 70 that is attached outside the phasedifference plate 60, below the light homogenization layer 50, and on aside of the light guide layer 30, and thus, is not leaked except throughthe light emitting surface 30 b but is propagated further in the lightguide layer 30.

Light emitted from the light source 11 is natural light, and variouspolarization components are mixed in the light. Hereinafter, the chainline with black circles in FIGS. 4A through 4C denotes a P-polarizationcomponent that vibrates on a plane such as a ground surface. Thelong-and-short broken line with arrows denotes an S-polarizationcomponent that vibrates on the plane perpendicular to the groundsurface. The S-polarization component is selectively emitted from thelight emitting surface 30 b by the polarization separation layer 40.

As described above, the polarization separation layer 40 includes thefirst fibers 41. As illustrated in FIG. 2A, the first fibers 41 have anextraordinary ray refractive index ne1 in a length direction and anordinary ray refractive index no1 in a cross-sectional direction. TheS-polarization component vibrates on a plane that is parallel to across-section of the first fibers 41 along the length direction.Accordingly, the S-polarization component may be affected by theextraordinary ray refractive index ne1 in the length direction of thefirst fibers 41, but not by the ordinary ray refractive index no1 in thecross-sectional direction.

On the other hand, as the P-polarization component vibrates on a planeparallel to the cross-section of the first fibers 41, it may be affectedby the ordinary ray refractive index no1 of the first fibers 41 in thecross-sectional direction. However, the P-polarization component is notaffected by the extraordinary ray refractive index ne1 of the firstfibers 41 in the length direction.

The first supporting medium 42 that supports the first fibers 41 isformed to correspond to the refractive index of the first fibers 41.Accordingly, when light is incident from the first supporting medium 42to the first fibers 41 or from the first fibers 41 to the firstsupporting medium 42, a P-polarization component propagates in amaterial of the same refractive index. Accordingly, the P-polarizationcomponent of light proceeds straight without being affected by therefractive index. In other words, the P-polarization component of lightmay propagate inside the first supporting medium, 42 in the same manneras when the first fibers 41 are not included. Accordingly, theP-polarization component denoted by the chain line of FIG. 4 is notrefracted by the first fibers 41, and thus, is reflected under aninternal total reflection condition of the first supporting medium 42.

On the other hand, the first supporting medium 42 has a refractive indexthat is different from the refractive index of the first fibers 41.Accordingly, when light is incident from the first supporting medium 42to the first fibers 41 or from the first fibers 41 to the firstsupporting medium 42, the S-polarization component propagates in amaterial of a different refractive index. Accordingly, theS-polarization component is affected by the refractive index and isrefracted or reflected. The S-polarization component denoted by thelong-and-short broken line of FIG. 4 is refracted or reflected by thefirst fibers 41 and a portion thereof deviates from an internal totalreflection condition of the first supporting medium 42 and is incidenton an interface at an acute angle and is emitted from the firstsupporting medium 42.

By stacking the polarization separation layer 40 on the light guidelayer 30, only an S-polarization component may be selectively scatteredand be emitted from the light emitting surface 30 b. As a result, apolarization component that is necessary for a liquid crystal unit maybe selectively emitted.

Above is described the first supporting medium 42 having a refractiveindex nm1 that corresponds to the ordinary ray refractive index no1 ofthe first fibers 41 and that is different from the extraordinary rayrefractive index ne1 of the first fibers 41.

However, the refractive index nm1 of the first supporting medium 42 maybe formed to correspond to the extraordinary ray refractive index ne1and to the ordinary ray refractive index no1 of the first fibers 41. Inthis case, only a P-polarization component may be selectively scatteredto be emitted from the light emitting surface 30 b. However, scatteringefficiency may be improved when using an S-polarization component thatdoes not vibrate within the same plane as the light guide direction oflight instead of using a P-polarization component that vibrates in thesame plane of the light guide direction of light. Accordingly, therefractive index nm1 of the first supporting medium 42 may be set tocorrespond to the ordinary ray refractive index no1 of the first fibers41.

The principle of diffusing light in the light guide layer 30 in anin-plane direction by using the light homogenization layer 50 will bedescribed below. FIG. 5 is a bottom view of the surface light sourceapparatus 1 of FIG. 1.

As illustrated in FIG. 5, the light sources 11 formed of LEDs emit lightas a point light source. Thus, a light amount between adjacent lightsources 11 may be reduced and dark portions may be generated in an area12 near the light sources 11. As light propagating in the light guidelayer 30 is scattered in the in-plane direction, light directiondistribution in the light guide layer 30 may be homogenized.Accordingly, some of the dark portions may disappear.

The light homogenization layer 50 includes the second fibers 51 asdescribed above. The second fibers 51 include an extraordinary rayrefractive index ne₂ in a length direction and an ordinary rayrefractive index no₂ in a cross-sectional direction. The second fibers51 are arranged such that a length direction thereof corresponds to alight guide direction of light. Accordingly, light incident on thesecond fibers 51 is influenced by the ordinary ray refractive index no1and the effective extraordinary ray refractive index ne2_eff.

As illustrated in FIG. 2B, when light that is guided in the lengthdirection of the second fibers 51 in the light homogenization layer 50is incident to the second fibers 51 at an incident angle θ, theeffective extraordinary ray refractive index ne₂ _(—) _(eff) may beexpressed as Equation (A):

$\begin{matrix}{{ne}_{2{\_ eff}} = \frac{{ne}_{2} \cdot {no}_{2}}{\sqrt{{{ne}_{2}^{2}\cos^{2}} + {{no}_{2}^{2}\sin^{2}\theta}}}} & (A)\end{matrix}$

In Equation (A), no₂ denotes the ordinary ray refractive index of thesecond fibers 51, and ne₂ denotes the extraordinary ray refractive indexof the second fibers 51, and θ denotes an incident angle of light withrespect to the second fibers 51 (length direction).

The P-polarization component vibrates along a plane parallel to across-section of the second fibers 51 in the length direction.Accordingly, the P-polarization component may be influenced by theeffective extraordinary ray refractive index ne2_eff of the secondfibers 51 in the length direction, but is not influenced by the ordinaryray refractive index no2 along the cross-sectional direction.

On the other hand, the S-polarization component vibrates along the planeparallel to the cross-section of the second fibers 51. Accordingly, theS-polarization component may be influenced by the ordinary rayrefractive index no2 of the second fibers 51 in the cross-sectionaldirection but is not influenced by the effective extraordinary rayrefractive index ne2_eff of the second fibers 51 in the lengthdirection.

When light is incident from the second supporting medium 52 to thesecond fibers 51 or from the second fibers 51 to the second supportingmedium 52, the P-polarization component is influenced by the effectiveextraordinary ray refractive index ne2_eff and is refracted orreflected, and the S-polarization component is influenced by theordinary ray refractive index no2 and is refracted or reflected. Thesecond fibers 51 are arranged in the light homogenization layer 50 suchthat the length direction thereof is parallel to the light guidedirection. Accordingly, an interface between the second fibers 51 andthe second supporting medium 52 does not lie at a right angle to thelight guide direction, and when the P-polarization component or theS-polarization component is refracted or reflected in the correspondinginterface, angle distribution in the in-plane direction of light varies.In other words, light may be inclined on the right and left sides of thelight guide direction. Accordingly, light propagating in the light guidelayer 30 is scattered and diffused at various angles, therebyhomogenizing the light direction distribution.

Light is refracted and extended only in a horizontal, left and rightdirection in the light homogenization layer 50, but the angle in avertical direction does not vary. Accordingly, both of the P- andS-polarization components do not satisfy the total internal reflectioncondition due to the light homogenization layer 50. For example, lightextends in the horizontal, left and right direction in the lighthomogenization layer 50 so as to remove only spots of an LED, and arefraction angle in the vertical direction in the polarizationseparation layer 40 varies such that only the S-polarization componentmay be emitted from the polarization separation layer 40. Accordingly, adesired polarization component may be emitted from the light guidepanel, and also light spots of the LED may be removed.

To perform the light homogenizing function, the refractive index nm2 ofthe second supporting medium 52 may be different from the ordinary rayrefractive index no2 and the extraordinary ray refractive index net ofthe second fibers 51.

However, the light homogenization layer 50 may be act more intensely asa homogenization layer of S-polarization.

The ordinary ray refractive index no2 and the refractive index nm2 ofthe second supporting medium 52 may have a difference of 0.03 orgreater, and for example, 0.05 or greater or 0.1 or greater.

To scatter and diffuse both the S- and P-polarization components with aproper balance, the ordinary ray refractive index no2 and theextraordinary ray refractive index ne2 of the second supporting medium52 and the refractive index nm2 of the second supporting medium 52 maysatisfy Equation (1) below:no₂<nm₂<ne₂   (1)

In particular, the refractive index nm2 of the second supporting medium52 and the effective extraordinary ray refractive index ne2_eff of thesecond fibers 51 may satisfy Equation (2) below:no₂<nm₂<ne₂ _(—) _(eff)   (2)

The refractive index nm2 of the second supporting medium 52 may satisfyEquation (3) below. The refractive index nm2 of the second supportingmedium 52 is smaller than the effective extraordinary ray refractiveindex ne2_eff of the second fibers 51, and thus the P-polarizationcomponent may be scattered and diffused. Accordingly, the secondsupporting medium 52 may function as a light homogenization layer thateffectively scatters and diffuses both the P- and S-polarization.

$\begin{matrix}{{no}_{2} < {nm}_{2} < \sqrt{\frac{{{ne}_{2}^{2} \cdot {no}_{2}^{2}} - {{ne}_{2}^{2} \cdot {nl}^{2}} + {{no}_{2}^{2} \cdot {nl}^{2}} + {ne}_{2}^{2} - {no}_{2}^{2}}{{no}^{2}}}} & (3)\end{matrix}$

In Equation (3), no2 denotes the ordinary ray refractive index of thesecond fibers 51, and ne2 denotes the extraordinary ray refractive indexof the second fibers 51, and nl denotes the refractive index of thelight guide layer 30.

Equation (3) is derived from Equation (2) and Equation (A) and Equations(B) through (F).

$\begin{matrix}{\frac{\sin\;\theta_{i}}{\sin\;\theta_{1}} = {\frac{nl}{ni} \approx {nl}}} & (B) \\{\frac{\sin\;\theta_{in}}{\sin\;\theta_{out}} = \frac{{nm}_{2}}{nl}} & (C) \\{\theta = {\frac{\pi}{2} - \theta_{out}}} & (D) \\{\theta_{1} = {\frac{\pi}{2} - \theta_{in}}} & (E) \\{{ne}_{2{\_ eff}} = \sqrt{\frac{{{ne}_{2}^{2} \cdot {no}_{2}^{2}} - {{ne}_{2}^{2} \cdot {nl}^{2}} + {{no}_{2}^{2} \cdot {nl}^{2}} + {ne}_{2}^{2} - {no}_{2}^{2}}{{no}^{2}}}} & (F)\end{matrix}$

In Equations (B) through (F) above, no₂ denotes the ordinary rayrefractive index of the second fibers 51, ne2 denotes the extraordinaryray refractive index of the second fibers 51, ni denotes a refractiveindex of an external medium of the light guide panel 20, nl denotes arefractive index of the light guide layer 30, θi denotes an incent angleof light incident on the light guide layer 30, θl denotes a refractionangle of light incident on the light guide layer 30, θin denotes anincident angle of light incident on the light homogenization layer 50,and θout denotes a refraction angle of light incident on the lighthomogenization layer 50. The light guide panel 20 is usually disposed inair, and a refraction index ni of an external medium of the light guidepanel 20 is the same as the refractive index of air(=1) and is expressedby Equation (B).

Equation (F) is derived in Equation (A) by substituting nm2 asnm2=ne2_eff and modifying Equation (A) using Equations (B) through (E).Equation (3) is derived from Equation (2) and Equation (F).

If nm2=ne2_eff, an incident light component (θ≈π/2) having a maximumangle among P-polarization does not proceed linearly without beingrefracted or reflected by the second fibers 51 of the lighthomogenization layer 50. Accordingly, the light homogenization layer 50may not perform the function of light homogenization with respect to thesame light component. An effective refractive index of light of theincident light component, which has an angle smaller than the maximumangle, is close to the ordinary ray refractive index no2.

When Equations (B) through (F) are all satisfied, light homogenizationwith respect to an incident light component incident to the secondfibers 51 at all angles θ may be performed.

When nm2 and the refractive index ne2_eff denoted by Equation (F) have adifference in refraction of 0.03 or greater, the effect of the lighthomogenization layer of the P-polarization component may be furtherimproved.

As illustrated in FIG. 5, a density of the second fibers 51 disposed ona central line between adjacent light sources 11 may be greater than adensity of the second fibers 51 disposed on an axis in a light emittingdirection of the light source 11 in the light homogenization layer 50. Alight amount between adjacent light sources 11 may be reduced and darkportions may be likely to be generated in the area 12 near the lightsources 11. Accordingly, by densely arranging the second fibers 51between the light sources 11, a light homogenization effect may befurther improved.

The first fibers 41 are arranged in the polarization separation layer 40such that the length direction of the first fibers 41 lies at a rightangle to a light guide direction. Accordingly, a cross-section of thefirst fibers 41 in a diameter direction may be substantially uniform inany position. As the first fibers 41 hardly vary in form in the lengthdirection, when the P- or S-polarization component is refracted orreflected by the first fibers 41, light is substantially not scatteredon both sides of the light guide direction even when seen from theplane. Light is scattered in the plane according to the light guidedirection. Angle distribution in the in-plane direction does not varysubstantially.

Light may be scattered in the in-plane direction by the second fibers 51that extend in a direction perpendicular to the incident surface 30 a inthe light homogenization layer 50. Accordingly, light may be scatteredin the in-plane direction, which may not be performed by using just aPSSE of the first fibers 41 that extend in parallel to the incidentsurface 30 a.

If the S-polarization component is emitted only, light at a phase nearto the P-polarization component remains in the light guide layer 30. Toalso use the remaining light effectively, the phase difference plate 60is disposed.

In FIG. 1, the phase difference plate 60 is a λ/4 plate and has athickness changing phases of light that is incident to the phasedifference plate 60 at right angles by 90 degrees. Light that is totallyreflected internally in the light guide layer 30 is not incident to thephase difference plate 40 at a right angle, as shown in FIG. 4.

Conversely, although the S-polarization component is sometimes convertedinto the P-polarization component, since the S-polarization component isselectively emitted to the outside, a ratio of conversion from theP-polarization component to the S-polarization component is high. Assuch, the remaining light in the light guide layer 30 is also convertedto the S-polarization component, and thus, emission efficiency of theS-polarization component may be increased and light usage efficiency maybe improved as a result.

The phase difference plate 40 may be used according to a wavelengthband. For example, a birefringence sheet formed by drawing a film formedof, for example, PC, polysulfide (PS), PMMA, polyvinyl alcohol,polyamide, polyester, etc. or a support sheet of a liquid crystalpolymer orientation layer, or a multi-layer stack structure may be usedas the phase difference plate 40. A sheet formed by arranging the firstor second fibers 41 or 51 used in the polarization separation layer 40or the light homogenization layer 50 in a supporting medium may be usedas the phase difference plate 40.

<Second Embodiment>

FIG. 6 is a side view of a surface light source apparatus 1 according toanother example embodiment.

In FIG. 4, the light homogenization layer 50 is below the light guidelayer 30. However, the position of the light homogenization layer 50 mayvary. The light homogenization layer 50 may be stacked on the lightguide layer 30. Thus, as in the surface light source apparatus 1illustrated in FIG. 6, the light homogenization layer 50 may also bebetween the light guide layer 30 and the polarization separation layer40.

<Third Embodiment>

FIG. 7 is a side view of a surface light source apparatus 1 according toanother example embodiment.

In the surface light source apparatus 1 illustrated in FIG. 7, the lighthomogenization layer 50 may be on the polarization separation layer 40.

<Fourth Embodiment>

FIG. 8 is a side view of a surface light source apparatus 1 according toanother example embodiment.

Referring to FIG. 4, the phase difference plate 60 is mounted on a sideopposite to the incident surface 30 a of the light guide layer 30.However, the phase difference plate 60 may be mounted on a principalsurface of the light guide layer 30 opposite to a surface on which thepolarization separation layer 40 is stacked. Also, the phase differenceplate 60 may be mounted on at least one side besides the incidentsurface 30 a of the light guide layer 30.

For example, like the surface light source apparatus 1 illustrated inFIG. 8, the phase difference plate 60 may be disposed on the principalsurface of the light guide layer 30 opposite to the surface on which thepolarization separation layer 40 is formed, for example, on a lowersurface of the light guide layer 30. However, when the phase differenceplate 60 is on the principal surface or the side of the light guidelayer 30 that is perpendicular to the light guide direction of light asillustrated in FIG. 8, the phase difference plate 60 is a λin plate, andmay have a thickness changing a phase of light incident to the phasedifference plate 60 by 180 degrees.

Accordingly, when light is refracted or reflected by the polarizationseparation layer 40 toward the light guide layer 30, or is incident tothe phase difference plate 60 at an acute angle, a phase of light variesby about 180 degrees, and thus the S-polarized light is maintained.Thus, the S-polarized light is reflected by the reflection plate 70,returns to the light guide layer 30, and is emitted from thepolarization separation layer 40. Thus, the S-polarized light isemitted, and light of the P-polarized light is prevented from beingemitted.

As described above, light that propagates in the light guide layer 30 isusually not incident on the phase difference plate 60 at a right angle,and thus is converted from the P-polarization component to theS-polarization component by the λon phase difference plate 60.

<Fifth Embodiment>

FIG. 9 is a side view of a surface light source apparatus according toanother example embodiment.

The surface light source apparatus illustrated in FIG. 9 includes apolarization separation light homogenization layer 80.

In the first through fourth example embodiments described above, thepolarization separation layer 40 and the light homogenization layer 50are separately included.

However, as illustrated in FIG. 9, the surface light source apparatusmay include the polarization separation light homogenization layer 80that is formed by integrating the polarization separation layer 40 andthe light homogenization layer 50.

Referring to FIG. 9, the polarization separation light homogenizationlayer 80 includes first fibers 81 and second fibers 82, and a thirdsupporting medium 83 that supports the first and second fibers 81 and82. The first fibers 81 extend parallel to the incident surface 30 a ofthe light guide layer 30, and the plurality of first fibers 81 arearranged in a direction perpendicular to the incident surface 30 a. Thesecond fibers 82 extend in a direction perpendicular to the incidentsurface 30 a, and the plurality of second fibers 82 are arranged in adirection parallel to the incident surface 30 a. For example, the firstfibers 81 and the second fibers 82 extend and are arranged in directionsat right angles to each other, and while the first and second fibers 81and 82 are woven with each other, they are supported by the thirdsupporting medium 83.

In the polarization separation light homogenization layer 80, anordinary ray refractive index no1 and an extraordinary ray refractiveindex ne1 of the first fibers 81, an ordinary ray refractive index no2and an extraordinary ray refractive index neo2 of the second fibers 82,and a refractive index n_(matrix3) of the third supporting medium 83satisfy Equations (4) and (5) below:no₁=n_(matrix3)<ne_(l)   (4)no₂<n_(matrix3)=ne₂   (5)

Accordingly, the first fibers 81 (warp threads) selectively scatter onlyan S-polarization component and emit the same through a light emittingsurface that is an upper surface of the polarization separation lighthomogenization layer 80. The second fibers 82 (woof) diffuse lightpropagating in the light guide layer 30 in an in-plane direction tohomogenize a light direction distribution. A refractive index nmatrix3of the third supporting medium 83 may correspond to the ordinary rayrefractive index no1 of the first fibers 81 and may be different fromthe extraordinary ray refractive index ne1 of the first fibers 81. Thus,the P-polarization component may not be refracted by the first fibers 81but proceed straight, and only the S-polarization component may beinfluenced by the extraordinary ray refractive index ne1 of the firstfibers 81 and a portion thereof may be emitted through the lightemitting surface.

On the other hand, the refractive index nmatrix3 of the third supportingmedium 83 may be different from the ordinary ray refractive index notand the extraordinary ray refractive index ne2 of the second fibers 82.Accordingly, the S-polarization component may not be refracted by thesecond fibers 82 but proceed straight, and only the P-polarizationcomponent may be influenced by the extraordinary ray refractive indexne1 of the second fibers 82 and be refracted and reflected to bediffused in the in-plane direction.

As the first and second fibers 81 and 82, the first and second fibers 41and 51 described above may be used, and the first supporting medium 42or the second supporting medium 52 may be used as the third supportingmedium 83. However, in an example embodiment, in order to satisfyEquations (4) and (5), the first fibers 81 and the second fibers 82 maybe formed of different materials.

<Sixth Embodiment>

FIG. 10 is a side view of a surface light source apparatus 1 accordingto another example embodiment.

In the first through fifth embodiments (FIGS. 1 through 9), the lightguide layer 30 is formed of a material different from the firstsupporting medium 42 and the second supporting medium 52.

However, the light guide layer 30 may be formed of the same material asa material of at least one of the first supporting medium 42 and thesecond supporting medium 52.

A light guide layer 34 in the surface light source apparatus 1illustrated in FIG. 10 corresponds to the light guide layer 30 of thesurface light source apparatus 1 of FIG. 1 and is formed of the samematerial as the first supporting medium 42. For example, the light guidelayer 34 may be regarded as the light guide layer 30 and thepolarization separation layer 40 according to the example embodiment ofFIG. 1 integrated into a single layer.

Although not shown in the drawings, the light guide layer 30 of thesurface light source apparatus 1 may be formed of the same material asthe second supporting medium 52 so that the light guide layer 30 and thelight homogenization layer 50 are integrated into a single layer.Although not shown in the drawings, in the surface light sourceapparatus 1 of FIG. 1, the light guide layer 30, the first supportingmedium 42, and the second supporting medium 52 may all be formed of thesame material so that the light guide layer 30, the polarizationseparation layer 40, and the light homogenization layer 50 areintegrated into a single layer.

In the surface light source apparatus of FIG. 9, in which thepolarization separation light homogenization layer 80 is formed byintegrating the polarization separation layer 40 and the lighthomogenization layer 50, the light guide layer 30 may be formed of thesame material as the third supporting medium 83 to integrate thepolarization separation light homogenization layer 80 and the lightguide layer 30 into a single layer.

By integrating the light guide layer 30 with the polarization separationlayer 40 and/or the light homogenization layer 50, manufacturing may besimplified and manufacturing costs may be reduced, and both a lightguide panel and a surface light source apparatus having a thin thicknessmay be manufactured.

The first fibers 41 are arranged in an upper portion of the light guidelayer 34 of FIG. 10. Alternatively, the first fibers 41 may be arrangedthroughout light guide layer 34, or in an area different from the upperportion of the light guide layer 34.

<Seventh Embodiment>

FIG. 11 is a side view of a surface light source apparatus 1 accordingto another example embodiment.

In the surface light source apparatus 1 according to the first throughsixth example embodiments, the light source unit 10 is on a side along ashort-axis of the light guide layer 30 constituting the light guidepanel 20.

However, the surface light source apparatus 1 may include a plurality oflight source units 10. For example, as illustrated in FIG. 11, the lightsource units 10 may be disposed on both sides along the short-axis ofthe light guide layer 30.

The surface light source apparatus 1 illustrated in FIG. 11 correspondsto the surface light source apparatus 1 of FIG. 8, except that the lightsource units 10 are on a side of the surface light source apparatus 1illustrated in FIG. 11 instead of the reflection plate 70.

Although not shown in the drawings, in some of the above-describedexample embodiments t, for example, in the surface light sourceapparatuses 1 of the first, second, and fourth embodiments, the lightsource units 10 may be disposed on both sides along the short-axis ofthe light guide layer 30. For example, the light source units 10 mayface each other with respect to the light guide layer 30.

The light source units 10 may be further disposed on a side besides alight-emitting surface of a long-axis of the light guide layer 30.

EXPERIMENTAL EXAMPLES

Experimental examples conducted to verify the effects of the surfacelight source apparatuses according to some example embodiments and acomparative example are described. The technical scope is not limited tothe experimental examples.

Experimental Example 1

Preparation of Light Guide Layer

As a light guide layer, PMMA (size: 6 cm×9 cm) was prepared.

(2) Formation of Polarization Separation Layer

As a first fiber, PET fibers (material: PET, no=1.5449, ne=1.7200, asurface roughness of external circumferential surface (Rz)=2 μm,cross-section: circular (diameter: 20 μm)) were arranged to a thicknessof fifteen layers in one direction on an upper surface of the preparedlight guide layer. As a first supporting medium designed to have arefractive index of 1.545 after curing, a UV curable resin waspenetrated between the PET fibers. A mixture of 40 parts by weight ofEA-F5503 available by Osaka Gas Chemicals Co., Ltd.; 58 parts by weightof MK esterA-400 available by Shin Nakamura Chemical Co., Ltd.; and 2parts by weight of Photopolymer Initiator Irgacure available by ShibaSpecialty Chemicals was used as the UV curable resin. The air betweenthe PET fiber and the UV curable resin was removed by vacuum degassing,and then the UV curable resin was covered with a released glass plate,and a UV lamp was used to cure the UV curable resin. The glass plate wasexfoliated to form a polarization separation layer on the light guidelayer.

When observing a cross-section of the polarization separation layerusing a laser microscope (available by Keyence Corporation VK-9600), asillustrated in FIG. 11, the polarization separation layer has astructure in which the first fibers arranged in one direction aresupported by the UV curable resin.

(3) Formation of Light Homogenization Layer

As a second fiber, N610 fibers (material: Nylon 6,10, no=1.5217,ne=1.5711, cross-section: circular (diameter: 50 μm)) were arranged on alower surface of the prepared light guide layer in three layers in adirection perpendicular to the arrangement direction of the first fibersof the polarization separation layer. As a second supporting mediumdesigned to have a refractive index of 1.571, a UV curable resin waspenetrated between the N610 fibers. A mixture of 40 parts by weight ofEA-F5503 available by Osaka Gas Chemicals Co., Ltd.; 58 parts by weightof MK esterA-400 available by Shin Nakamura Chemical Co., Ltd., and 2parts by weight of Photopolymer initiator Irgacure available by ShibaSpecialty Chemicals may be used as the UV curable resin. By curing theUV curable resin in the same manner as when forming the polarizationseparation layer, a light homogenization layer was formed on the lightguide layer.

(4) Arrangement of Light Source Unit, Phase Difference Plate, andReflection Plate

A light source unit including nine LEDs as light sources arranged in onedimension (serial arrangement) is installed along a short-axis of thelight guide layer. The side at which the light source unit is installedis set to be parallel to the length direction of the first fibers of thepolarization separation layer, and perpendicularly to the lengthdirection of the second fibers of the light homogenization layer, andthe arrangement direction of the LEDs is set to be in a directionparallel to the length direction of the first fibers of the polarizationseparation layer. Then, a λse phase difference plate is arranged at aside of the light guide layer opposite to the side where the lightsource unit is installed. Also, a reflection plate is mounted on allsurfaces except an upper surface of the polarization separation layer(light-emitting surface) and the side on which the light source unit isinstalled. Consequently, the surface light source apparatus wasmanufactured. The surface light source apparatus according toExperimental example 1 corresponds to the surface light source apparatusof the example embodiment illustrated in FIG. 1.

Experimental Example 2

A light homogenization layer was formed on the upper surface of thelight guide layer. The surface light source apparatus was manufacturedin the same manner as Experimental example 1 except that PET fibers(PET, no=1.5449, ne=1.7200, a surface roughness of externalcircumferential surface (Rz)=2 μm, cross-section: circular (diameter: 20μm)) were used as the second fiber, and a UV curable resin designed tohave a refractive index of 1.605 after curing was used as the secondsupporting medium. A mixture of 68 parts by weight of EA-F5503 availableby Osaka Gas Chemicals Co., Ltd.; 30 parts by weight of benzylacrylate;and 2 parts by weight of Photopolymer Initiator Irgacure 184 availableby Shiba Specialty Chemicals may be used as the UV curable resin.

The surface light source apparatus manufactured according toExperimental example 2 corresponds to the surface light source apparatus1 illustrated in FIG. 6.

Experimental Example 3

A polarization separation layer was formed on the upper surface of alight guide layer. Except that a light homogenization layer was formedon the upper surface of the polarization separation layer, the surfacelight source apparatus was manufactured in the same manner asExperimental example 2.

The surface light source apparatus manufactured in Experimental example3 corresponds to the surface light source apparatus 1 illustrated inFIG. 7.

Experimental Example 4

A surface light source apparatus was manufactured in the same manner asExperimental example 2 except that PET fibers (PET, no=1.5449,ne=1.7200, a surface roughness of external circumferential surface(Rz)=2 μm, cross-section: equilateral triangular (each side length: 10um) were used as first fibers forming the polarization separation layer.

Comparative Example 1

A surface light source apparatus was manufactured in the same manner asExperimental example 1 except that a light homogenization layer was notformed.

[Evaluation]

In the surface light source apparatuses obtained in the experimentalexamples and Comparative example 1, a luminance of light emitted fromthe light emitting surface and luminance spots and a polarization of thelight were measured. The luminance, the luminance spots, and thepolarization were measured by using a two-dimensional colorimeter,Konica Minolta CA-2000 or Conoscope 80 available by AUTRONIC-MELCHERSGmbH in combination with a polarization plate to calculate a ratio of adesired polarization component. A luminance was measured by driving theserially-arranged nine LEDs with a constant current of 30 mA. As theluminance of emitted light, front luminance in the center of thelight-emitting surface of the light guide panel was measured. Table 2below shows the measurement result.

Referring to FIGS. 13 and 14, two-dimensional luminance distribution oflight emitted from an upper surface of the light guide panel(light-emitting surface) of the surface light source apparatusesmanufactured according to Experimental example 2 and Comparative example1 measured by CA-2000 is shown. The same two-dimensional luminancedistribution as that shown in FIG. 13 may be obtained from the surfacelight source apparatuses manufactured according to Experimental examples1, 3, and 4.

TABLE 2 Stacking order of light homogenization layer, light light guidepolarization homogenization Evaluation layer, and separation layer layerPolarization polarization First Second (s separation First supportingSecond supporting Luminance Luminance polarization:p layer fiber mediumfiber medium spots (cd/m²m²) polarization) Experimental Light no = 1.545nm₁ = 1.545 no = nm₂ = 1.571 No 1200 16:1 Example 1 homogenization ne =1.720 1.5217 stripe layer, ne = 1.5711 spots in light guide light layer,polarization separation layer Experimental Light guide no = nm₁ = 1.545no = nm₂ = 1.605 No 1400 15:1 Example 2 layer, light 1.545 1.545 stripehomogenization ne = 1.720 ne = spots in layer, 1.720 light polarizationseparation layer Experimental Light guide no = 1.545 nm₁ = 1.545 no =1.545 nm₂ = 1.605 No 1300 10:1 Example 3 layer, ne = 1.720 ne = 1.720stripe polarization spots in separation light layer, lighthomogenization layer Experimental Light guide no = nm₁ = 1.545 no =1.545 nm₂ = 1.605 No 2900 15:1 Example 4 layer, light 1.545 ne = 1.720stripe homogenization ne = spots in layer, 1.720 light polarizationseparation layer Comparative Light guide no = nm₁ = 1.545 — No 1000 16:1example 1 layer, 1.545 stripe polarization ne = 1.720 spots inseparation light layer

In the surface light source apparatuses of Experimental examples 1through 4 in which the light homogenization layer is included, asillustrated in FIG. 13, stripe spots are not observed in light emittedfrom the upper surface of the stacked structure. Thus, as can be seenfrom this result, according to the surface light source apparatuses ofsome of the example embodiments, luminance spots are removed when anLED, which is a discontinuous light source, is used. According to thesurface light source apparatuses manufactured according to the aboveexperimental examples, high polarization separation performance may beobtained.

In the surface light source apparatus manufactured according toComparative example 1, a ratio of polarization separation is similar tothat of Experimental examples. However, as illustrated in FIG. 14,stripe spots are clearly observed in light emitted from the uppersurface of the stacked structure.

In the surface light source apparatus of Experimental example 4 in whichthe first fibers of the polarization separation layer have anequilateral triangular cross-section, an intensity (luminance) of lightemitted in a direction perpendicular to the light guide layer (lightemitted from the upper surface of the stacked structure) is twice aslarge as that in the surface light source apparatus of Experimentalexample 2 in which the first fibers have a circular cross-section.

As described above, according to at least one of the exampleembodiments, the surface light source apparatuses have excellentpolarization separation performance, and, even when a discontinuouslight source such as an LED is used, stripe spots of light may beprevented.

Hereinafter, a flat panel display according to an example embodimentwill be described.

The flat panel display includes a liquid crystal panel on which an imageis formed and a light source apparatus that supplies light used indisplaying the image to the liquid crystal panel. The light sourceapparatus may be a surface light source apparatus according to theexample embodiments. The liquid crystal panel may be on a surface fromwhich light of the surface light source apparatus is emitted. The liquidcrystal panel may be a typical liquid crystal panel.

It should be understood that the example embodiments described hereinshould be considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each exampleembodiment should typically be considered as available for other similarfeatures or aspects in other example embodiments.

What is claimed is:
 1. A light guide panel comprising: a light guidelayer having a light incident surface; a polarization separation layerconfigured to select a desired polarization among light emitted from thelight guide layer and to emit light having the desired polarization; anda light homogenization layer including a plurality of first fibers and afirst supporting medium of the first fibers, the light homogenizationlayer configured to diffuse and scatter light incident on the lightincident surface into the light guide layer.
 2. The light guide panel ofclaim 1, wherein the polarization separation layer comprises: aplurality of second fibers having birefringence; and a second supportingmedium that is isotropic and configured to support the second fibers. 3.The light guide panel of claim 2, wherein a refractive index of thesecond supporting medium corresponds to at least one of two differentrefractive indices of the second fibers.
 4. The light guide panel ofclaim 1, wherein the polarization separation layer comprises: aplurality of second fibers having birefringence; and a second supportingmedium that is isotropic and configured to support the second fibers;and wherein the plurality of first fibers have birefringence, and thefirst supporting medium is isotropic and configured to support the firstfibers.
 5. The light guide panel of claim 4, wherein a refractive indexof the first supporting medium is different from at least one of the twodifferent refractive indices of the first fibers.
 6. The light guidepanel of claim 4, wherein an ordinary ray refractive index no₂ and anextraordinary ray refractive index ne₂ of the first fibers and arefractive index nm₂ of the first supporting medium satisfy Equation (1)below:no₂<nm₂<ne₂  (1).
 7. The light guide panel of claim 2, wherein a surfaceroughness Rz of an outer circumferential surface of the second fibers isfrom about 0.1 μm to about 10 μm.
 8. The light guide panel of claim 2,wherein the second fibers have a polygonal cross-section in a radiusdirection.
 9. The light guide panel of claim 4, wherein one of the lightguide layer, the polarization separation layer, and the lighthomogenization layer is between the remaining two layers.
 10. The lightguide panel of claim 2, further comprising: a phase difference plateconfigured to convert a polarization direction of light in the lightguide layer; and a reflection plate on a surface other than (i) thelight incident surface and (ii) a light emitting surface of the lightguide layer, the reflection plate configured to reflect light emittedfrom the light guide layer back into the light guide layer.
 11. Thelight guide panel of claim 9, wherein the polarization separation layerand the light homogenization layer are on the light emitting surface ofthe light guide layer.
 12. The light guide panel of claim 11, whereinthe polarization separation layer and the light homogenization layer areintegrated into a single layer.
 13. The light guide panel of claim 12,wherein in the single layer, the first fibers and the second fibersalternate, and a third supporting medium includes the first and secondsupporting media and is configured to support the first and secondfibers.
 14. The light guide panel of claim 12, further comprising: aphase difference plate configured to convert a polarization direction oflight in the light guide layer; and a reflection plate on a surfaceother than (i) the light incident surface and (ii) the light emittingsurface of the light guide layer, the reflection plate configured toreflect light emitted from the light guide layer back into the lightguide layer.
 15. The light guide panel of claim 9, wherein the lightguide layer is a same material as at least one of the first and secondsupporting media.
 16. The light guide panel of claim 13, wherein anordinary ray refractive index no₁ and an extraordinary ray refractiveindex ne₁ of the second fibers, an ordinary ray refractive index no₂ andan extraordinary ray refractive index ne₂ of the first fibers and arefractive index n_(matrix3) of the third supporting medium satisfyEquations (4) and (5) below:no₁=n_(matrix3)<ne₁  (4)no₂<n_(matrix3)=ne₂  (5).
 17. The light guide panel of claim 4, whereina density of the second fibers is higher away from the light incidentsurface.
 18. The light guide panel of claim 4, wherein a density of thefirst fibers varies according to arrangement positions.
 19. The lightguide panel of claim 4, wherein some of the plurality of first andsecond fibers comprise discontinuous portions.
 20. The light guide panelof claim 4, wherein portions of the plurality of first and second fibersoverlap.
 21. The light guide panel of claim 13, wherein the first fibersand the second fibers are different materials.
 22. A surface lightsource apparatus comprising: a light source unit including a pluralityof light sources spaced apart from one another; and a light guide panelconfigured to emit light having a polarization component of lightincident from the light source unit, wherein the light guide panel isone of claim
 1. 23. The surface light source apparatus of claim 22,wherein the polarization separation layer comprises: a plurality ofsecond fibers having birefringence; and a second supporting medium thatis isotropic and configured to support the second fibers; and whereinthe plurality of first fibers have birefringence, and the firstsupporting medium is isotropic and configured to support the firstfibers.
 24. The surface light source apparatus of claim 23, wherein adensity of the first fibers is higher between the plurality of lightsources.
 25. The surface light source apparatus of claim 22, wherein theplurality of light sources are on two opposite sides of the light guidepanel.
 26. The surface light source apparatus of claim 23, wherein oneof the light guide layer, the polarization separation layer, and thelight homogenization layer is between the remaining two layers.
 27. Thesurface light source apparatus of claim 23, further comprising: a phasedifference plate configured to convert a polarization direction of lightin the light guide layer; and a reflection plate on a surface except (i)the light incident surface and (ii) a light emitting surface of thelight guide layer, the reflection plate configured to reflect lightemitted from the light guide layer back into the light guide layer. 28.The surface light source apparatus of claim 26, wherein the polarizationseparation layer and the light homogenization layer are on the lightemitting surface of the light guide layer.
 29. The surface light sourceapparatus of claim 23, wherein the polarization separation layer and thelight homogenization layer are integrated as a single layer.
 30. Thesurface light source apparatus of claim 29, wherein in the single layer,the first fibers and the second fibers alternate, and a third supportingmedium includes the first and second supporting media and is configuredto support the first and second fibers.
 31. The surface light sourceapparatus of claim 29, further comprising: a phase difference plateconfigured to convert a polarization direction of light in the lightguide layer; and a reflection plate on a surface except (i) the lightincident surface and (ii) a light emitting surface of the light guidelayer, the reflection plate configured to reflect light emitted from thelight guide layer back into the light guide layer.
 32. The surface lightsource apparatus of claim 26, wherein the light guide layer is a samematerial as at least one of the first and second supporting media. 33.The surface light source apparatus of claim 23, wherein a density of thesecond fibers is higher away from the light incident surface.
 34. A flatpanel display comprising: a light source apparatus; and a liquid crystalpanel configured to display an image with light supplied from the lightsource apparatus, wherein the light source apparatus is the surfacelight source apparatus of claim
 22. 35. The flat panel display of claim34, wherein the plurality of first fibers have birefringence and thefirst supporting medium is isotropic and configured to support the firstfibers.
 36. The light guide panel of claim 1, wherein the lighthomogenization layer is provided in a lengthwise direction of the lightguide layer.
 37. The light guide panel of claim 36, wherein the lighthomogenization layer is provided substantially over an entire portion ofa surface of the light guide layer.
 38. The device of claim 14, whereinthe light homogenization layer is provided one of in a first directionperpendicular to the light incident surface and in a second directionwhich is inclined by about ±45° with respect to the first directionperpendicular to the incident surface .